Building With, Not For: How She Became a Bestseller by Creating the Portfolio Substackers Proudly Share
Build to Launch Friday: Meet Karo, the AI Product Manager Who Turned Creator Pain Points Into Community Gold
Welcome to Build to Launch Fridays, where we meet the builders turning domain expertise into AI-powered products.
Every Friday, I'm spotlighting someone from the vibe coding builders collection who's doing exactly what I believe is the future: using AI not as just another tool, but as a true collaborator to transform curiosity, passion, and years of professional knowledge into something scalable and ownable. No VC funding, no technical co-founders, no permission required, just domain experts who decided to build.
Today, meet — the AI Product Manager who built the community tool that Substack creators can't stop talking about.
As I was drafting this article, Karo officially became a Substack Bestseller! She shared that her community tool, Stackshelf, played a big role in making that happen. What a powerful validation of her work! Congratulations, many times over 🎉
What do you do when you notice a glaring gap in the ecosystem you live and breathe every day?
If you're Karo, you don't wait around for someone else to solve it. You build the solution yourself, through real feedback, iterations, and community input.
As an experienced AI Product Manager, Karo saw that Substack creators had incredible products but no elegant way to showcase them. So she built Stackshelf: a beautifully crafted, creator-first platform that’s quickly become a favorite across the Substack world.
Visit Stackshelf at https://stackshelf.app/
What stands out most is how she built it, not in isolation, but hand-in-hand with the very people it was meant to serve. From the early Notion prototype to a paid, production-ready tool, it grew through conversation, not speculation.
When I invited her to Vibe Coding Builders, it was obvious she got it: the future of building isn’t about hype, it’s about turning domain knowledge into real tools that serve real people.
In the Q&A below, you’ll see how Karo thinks, how she builds, and why her work resonates so deeply with the community she’s part of.
Background & Personal Journey
Can you tell me a bit about your background? Do you come more from the technical side or product management?
I never know how to answer that one, heheh. I’m not an engineer by trade, but I’ve been living in technical teams since I was 21, basically raised by them. For the past 8 years, I’ve been an AI Product Manager.
Do you have a full-time job? How did you balance that with building and maintaining Stackshelf?
Yes, I do work full-time, I’m also raising a family and raising a Substack. I don’t know how I balance it, I’m not even sure I do balance it 😂. But I love all three too much to stop.
Lol, I ask because it’s important… and I’m in the same boat too. Any bit of wisdom helps!
Origin of Stackshelf
You first hosted Substack products in Notion before moving to Stackshelf. How long did it stay there, and is that collection still around? Was starting on Notion intentional, or did you always plan to turn it into a product?
Yes, that's right. Notion was my garage - I started there just to see if anyone would actually submit their products. My deal with myself was: if nobody cares, I’ll quietly kill the idea. But they did care, and those early submissions - plus a few other signals - told me I was onto something. That collection has since moved into StackShelf. The old Notion page has been retired.
Great strategy! Early on (and sometimes now), I think of an idea, I just build. Now wonder how much time I could have saved keeping that in mind 😂
From the moment you decided to build, how long did it take you to launch?
It took about 13 long evenings to get it to pass user tests. The first test failed (the horror is documented here :), but the second one passed - and that’s when I was ready to invite more users in.
Yup, I read that story… funny how it’s always just a handful of bugs that end up taking half the total build time.
Building & Design Choices
You built Stackshelf on Replit, what tools or workflows did you lean on? Any overlooked features (like Assistant mode) that people should know about?
My workflow is a co-dependent combo of ChatGPT and Replit. ChatGPT is where I brainstorm and build prompts; Replit is where I actually build. I don’t use Assistant much, I prefer the Agent. Replit itself has a lot of useful features: deployments, databases, GitHub integration, even domain purchasing. Their latest update adds Agent roles (Plan or Build), which I’ve found super useful too.
Interesting to hear how differently people use it. leaned on Assistant mode to save credits, while Karo loved Agent mode, and I can see why. When I tried Replit myself, I found Agent mode super powerful, but I still like using Assistant for brainstorming, just to keep everything in one chat box.
My only complaint: I wish Assistant and Agent were combined in the same tab. That would make it so much easier to stay in flow.
The creator profiles are so clean and elegant. How did you land on that design style?
Thank you for saying that, I appreciate it :)
I knew that investing in this bento-style design would take longer to develop, but I didn’t want to compromise with a simple page of links. Creator profiles should be beautiful, attention-grabbing, and act as a showcase, something people are proud to share, not just functional placeholders.
I was never great at design, so this was a real wake-up call for me when working on VibeCodingBuilders. I’ve honestly learned a lot just by studying how others design their pages, and changed so much about how things are presented. Now I’ve got to look into bento-style design to see how I can bring that approach into the site.
The product images are beautiful too, did you create those yourself?
And how did you handle storing them on the backend?
Are most of the creator images managed by you personally?
Do you have users actively manage and update their own profiles?
Yes, everyone can manage their images in the dashboard, but some Creators are simply too busy, and I step in when needed. So it’s a mix: most product images are uploaded by Creators themselves, some are fetched automatically from URLs, and a few I’ve made.
Thanks, Karo. Guess I’m one of those “too busy” creators you had to step in for when it came to making some of the images 😅_._
Community & Growth
On the creators page, you mention people who “helped build Stackshelf.” What does that mean in practice?
These are the awesome people who spent their free time testing, finding bugs, making suggestions, and improving the product. Some, like , really pulled their weight. I actively encourage users to keep suggesting as they go - I don’t want to build for them, I want to build with them. And some, like Justin, and , have been especially great at providing thoughtful feedback.
Yes, I read their stories in your article, they’ve all been amazing. So generous with their time, and the value they’ve brought is incredible.
I noticed some creators have products and freebies, while others don’t. Was that by design to encourage participation?
By design, yes. StackShelf brings products that are already sold elsewhere (Gumroad, Amazon, etc.) closer to the Substack audience. It has to reflect the realities of creators: most offer freebies as lead magnets, alongside paid products to actually monetize.
You’re great at promoting others. What’s your strategy for promoting Stackshelf itself?
I have no idea yet - or, not entirely true. My hope is that creators will help promote it by sharing their shelf-in-bio links, which should kick-start the network effects. I haven’t touched paid ads. I really believe in the power of community.
Looks like your strategy is working, I’ve seen plenty of people sharing it already. ’s notes in particular really struck me.
Some creator pages link out to Buy Me a Coffee, freebies, personal sites, and more. Do you see Stackshelf as a kind of “footprint collector” for creators, a place to bring everything together?
Yes! Exactly! It’s about bringing everything together and closer to the Substack audience. Here’s me: my profile, my newsletter, my homepage, my freebies, my products… and if you feel like it, you can even buy me a coffee.
This is genius. I do wonder when you first came up with the idea… maybe it surfaced while you were actually building Stackshelf?
And yes, I’ll admit it: I’ve gradually stolen a few of those ideas myself for VibeCodingBuilders 😅_._
Business & Future Vision
Since you launched paid plans, do you already have premium users?
Yes, I do. Otherwise StackShelf wouldn’t be realistic. It’s a fully developed platform, which comes with real build and maintenance costs. Even with premium members, I’m still funding most of it out of my own pocket.
Thanks again, Karo, for not charging me back then. I honestly thought you weren’t charging anyone! It does make me reflect on VibeCodingBuilders though. I’d love to keep it free as long as possible, and it is for now. But as it grows, maybe sponsorships could be a good way to keep things sustainable.
Do you offer an affiliate program? How does that work?
Not yet, but I know I should. Once I have a bit more time, I’ll look into it.
For now, I’m relying on users to share StackShelf willingly.
I know that sounds naive, and that incentives should probably exist from day one, but many people are - rightly - proud of their shelf-in-bio. That kind of symbiosis helps.
I really love this community-driven model: people share because they’re genuinely proud of what they’ve built. And if that pride isn’t there, maybe the platform isn’t the right fit anyway.
I’ve seen something similar with VibeCodingBuilders: I never really pushed people to share, but some do it voluntarily, and I appreciate that so much.
The more we all share, the more the platform becomes a flywheel that lifts everyone up and makes us all more visible.
What’s been your biggest win since launching Stackshelf?
Having the first user come, stay, and drag others in with them - that’s peak happiness for a PM. We live for that stuff.
So true! I’d call that not just a PM’s peak happiness, but also a builder’s peak happiness too. I feel that myself right now.
Do you see it becoming your main newsletter foundation, and a flywheel for both you and creators?
I hope so - but I don’t want it to be the only flywheel. What’s clear is this: if Substack decided to launch a marketplace feature tomorrow (which, honestly, they should), StackShelf would cease to exist. So I need to prepare for that.
That worry is real. And it sounds like you already have a plan.
Are there hidden perks people might be missing?
Yes, the insights. Even now you can see how many people visit your shelf and how many actually click through to your sales page, that’s really useful.
Where do you see Stackshelf two years from now?
In the ideal scenario, every Substack creator uses it and it becomes the standard way to showcase books and offers. And ideal scenarios are generally the ones I prefer to focus on heheh.
Wow, ambitious, Karo! Love it!
Advice for Builders
For someone starting their first app today, what’s your number one warning?
Don’t touch a line of code until you have a requirements doc and a system prompt in place. I’ll be writing a blog post on why soon.
I relate to this so much! Having a clear requirements doc and prompt upfront saves sooo many headaches down the road.
Final Words
Talking with Karo reveals what really drives meaningful products today. Yes, tools like Replit and ChatGPT made the build possible., but mindset is the true differentiator.
Stackshelf wasn’t built in a vacuum. It started with a simple Notion page, evolved with community feedback, and became something people were proud to share. That humility — paired with real product chops — is what turned an experiment into a living, growing platform.
"I don't want to build for them, I want to build with them."
That spirit is exactly what we need more of: products rooted in lived experience, shaped by feedback, and sustained through shared pride, not just marketing tactics.
Karo’s not chasing scale for scale’s sake. She’s growing something sustainable, thoughtful, and useful. That’s exactly the kind of builder we celebrate inside Vibe Coding Builders.
If you’re turning your expertise into products, building with AI, or helping others do the same, you belong here. Join the vibe coding builders community and get featured on Build to Launch Friday. Curious why it all started? Here’s the full story behind Vibe Coding Builders.
If Karo’s story speaks to you, connect with her, you’ll only regret not knowing her earlier.
[
Product with Attitude
I'm an AI Product Manager who likes to build great tools for creators. I write about AI, product, UX & vibecoding and help you get featured on https://stackshelf.app/.
By Karo (Product with Attitude)
](https://karozieminski.substack.com?utm_source=substack&utm_campaign=publication_embed&utm_medium=web)
Now it’s your turn:
What ecosystem do you live in?
What obvious gaps do you see?
What knowledge are you sitting on that could become something real?
Karo turned her insight and empathy into a platform with paying users and natural momentum.
What will your builder story be?
— Jenny